On the third day of the battle even at night there was no break in fighting. It was a moon-lit night, and in spite of fatigue after three days' strenuous battle, the armies continued to fight.
It was now a war of stamina. Both sides were on the verge of human endurance, and whosoever could be steadfast for some time more was likely to win. Both the sides hoped that they were likely to win.
In the matter of stamina the refined Persians could be no match for the hardy Arabs. The strategy of Sa'ad was to wear down the Persians, and snatch away the victory from them.
The battle waged all the night long. About midnight, Qaqa shouted:
"We have strangled the enemy,
The enemy is now on the verge of collapse."
There were heavy casualties among the Persians, but they stood firm.
At sunrise the fighting ceased, but still the result was inconclusive. That was now the fourth day of the battle, and it was felt that it might be the last day of the battle. Qaqa addressed his men:
"If we fight for an hour or so more, the enemy will be defeated.
So, warriors of the Bani Tameem make one more attempt and victory will be yours."
Other Chiefs spoke in similar terms to their contingents. The Muslim warriors shouted "If you attack we are with you."
Qaqa hurled his contingent against the Persians with great violence. Seeing the Bani Tameem launch the attack, other Muslim contingents followed suit. The Persians too exhausted after continuous war for twenty-four hours were taken unawares at the resumption of battle. They stood up in battle formation to resist the Muslim charge, but now there were signs of weakness among the Persian ranks. The right wing of the Persians under Harmuzan was pushed back. After withdrawal they reformed and again stood their ground. By noon Qaqa and his men were able to pierce through the Persian centre. They dashed towards the Persian Headquarters to get hold of Rustam, the Commander-in-Chief of the Persian forces.
At this time a strong dust storm lashed the battle-field. The storm blew in the faces of the Persians, and aided the onward advance of the Muslims. The canopy and the throne of Rustam were blown away by the dust storm and thrown in the Ateeq. Rustam was alone. He moved back and sought shelter behind a mule which carried in saddle boxes his personal belongings. A Muslim warrior Hilal b. Ullafa saw the mule and struck at the saddle boxes with his sword. Owing to poor visibility, Hilal could not notice Rustam, nor was Rustam able to see Hilal. The saddle box fell on Rustam. He cleared the box and ran towards the river. Hilal now saw Rustam, and ran after him. Rustam plunged in the river. Hilal jumped in the river after him. He dragged him to the bank, where drawing his sword he struck several blows at Rustam and killed him. Then he dragged the corpse of Rustam and threw it under the feet of the mule. Hilal exultant at having killed the Commander-in-Chief of the Persian forces shouted:
"By the Lord of the Kaaba,
I have killed Rustam,
I am Hilal bin Ullafa."
The Persians were not aware of the death of Rustam, and they went on fighting doggedly.
When Sa'ad came to know that Rustam had been killed, he ordered the Muslims to make one more attack and drive away the Persians. In the afternoon the Muslims mounted another attack. By this time even the Persians knew that their Commander-in-Chief had been killed. That demoralised the Persians and after putting up a last heroic resistance, the Persian front collapsed. With the collapse, the Persian warriors fled in panic to the river.
The chained Persians arrived at the bank of the Ateeq anxious to fly to safety. The victorious Muslims followed at their heel. Some Persians were picked up by the Muslims with their long spears. Those who plunged in the river, because of the heavy weight of their armours and chains were unable to cross to the other bank and were drowned.
At this stage Jalinus took command of what was left of the Persian army. He got control of the bridge head, and succeeded in getting a section of the Persian army cross the bridge safely.
The battle of Qadisiyya was now over. Out of 60,000 Persians who had taken the field, only 20,000 survived to tell the story of the disaster that they had met at the battle-field of Qadisiyya. 40,000 Persians were killed or drowned. The Muslim casualties numbered 6,000 out of a total force of 30,000. In the case of the Persians, out of every three persons only one survived: in the case of Muslims out of every five Muslims four survived to rejoice at the victory.
Sad sent parties to pursue the fleeing Persians. The main Persian force commanded by Jalinus proceeded to Najaf. The pursuing Muslim party led by Zuhra caught up the Persians half way between Kharara and Seilahun. Brought to bay Jalinus choose to fight. He threw a challenge for a personal duel. The challenge was accepted by Zuhra. In the duel Jalinus was killed. Thereupon the Persians fled. They were pursued upto Najaf and the stragglers that the Muslims met in the way were put to sword. When it was night, Zuhra and his party returned to Qadisiyya.
Other parties sent in various directions also caught up flying Persians. Most of them were killed or taken catives.
The booty that the Muslims captured was vast. After setting aside the State share of one fifth, the rest was distributed among the men who had participated in the battle of Qadisiyya. Each infantry man received 7,000 dirhams, and each cavalryman 14,000 dirhams as his share.